A well-recognized technique for arterial bypass has been the use of an in situ vein, such as the saphenous vein. Whereas arteries have smooth, unobstructed interior surfaces, veins have valves which ensure a primary direction of blood flow. The direction of blood flow in an artery is determined by the pumping action of the heart, i.e. the blood flow is away from the heart. On the other hand, the primary blood flow direction in a vein is directly opposite that, i.e. toward the heart. The valve typically is composed of two leaflets opposite each other. In response to blood flow away from the heart, the opposed edges of the leaflets are brought together to impede this blood flow. Thus if a vein is to be used as an arterial bypass, the valves must be rendered inoperative, for they would otherwise obstruct the arterial flow of blood. Techniques and devices for rendering valves inoperative are described in the following U.S. and foreign patent documents:
______________________________________ Patent No. Name ______________________________________ 2,779,334 Sandborn 3,837,345 Matar 4,493,321 Leather 4,655,217 Reed 4,681,106 Kensey USSR 537,676 Shalimov UK 2,044,103 Ross ______________________________________
and in the following publications:
Kutz et al, "New Vein Stripper and Technique of Stripping", Surgery, February 1951, pp. 271 et seq;
Skagseth et al, "In Situ Vein Bypass", Scand J Thor Cardivosac Surg, 7:53-58, 1973;
Samuels, "In Situ Saphenous Vein Arterial Bypass", The American Surgeon, February 1968, Vol. 34, No. 2, pp. 122 et seq;
Mills, "Valvulotomy of Valves in the Saphenous Vein Graft Before Coronary Artery Bypass", J. Thorac. Cardiovasc. Surg., 76: 878-879, 1976; and
LeMaitre, In Situ Bypass Grafting, 1987.
Leather describes that it "has been found that the simplest, most expedient and least traumatic method of rendering the bicuspid venous valve incompetent is to cut the leaflets in their major axes while they were held in the functionally closed position by fluid flow or arterial pressure from above."
In order to accomplish this purpose, Leather describes that it is necessary to expose both proximal and distal sites of the vein. The proximal site is closer to the heart than the distal site. A rod is inserted through the distal incision and through the vein until it exits at the proximal incision. A valve cutter is attached to the rod and a catheter is sutured to the valve cutter. The valve cutter is then drawn into the vein through the proximal incision. Fluid supplied by the catheter keeps the valve leaflets closed during the retrograde motion of the cutter through the vein, i.e. from proximal to distal sites. The Russian Patent No. 537,676 describes a similar instrument.
Some of the valve cutters or valvulotomes use instruments of cylindrical form to render the valves inoperative. These instruments are designed to ride within the vein and disable the valve leaflets around their entire circumferential junction with the vein wall. Other valvulotomes use valve disrupting elements of planar form, e.g. Leather 4,493,321. A disadvantage of the planar form of instrument is that it is necessary to properly orient the instrument for maximum effectiveness. When the instrument is in use (within the vein) the surgeon is not in a position to visually observe the orientation relative to the valve leaflets. It is therefore another object of the present invention to provide a valvulotome in which the orientation of the disrupting element relative to the valve leaflets is no longer crucial for the effective operation of the instrument.